US6970564B1 - Data multiplexing device, program distribution system, program transmission system, pay broadcast system, program transmission method, conditional access system, and data reception device - Google Patents

Abstract

In a data multiplexing device which multiplexes and transmits the transport stream packets of program data consisting of a plurality of data elements constructed in the form of transport stream packets, a program distribution system, a program transmission system, a pay broadcast system, a program transmission method, a conditional access system, and a data reception device according to the present invention, by generating a scramble key Ks corresponding to one or more data elements among the plurality of data elements constituting a program and by scrambling each data element, an audience can subscribe for each data element.

Description

This is a division of copending application Ser. No. 09/370,776, filed Aug. 9, 1999, which is a continuation of application no. PCT/JP98/03127 filed Jul. 13, 1998.

TECHNICAL FIELD

The present invention relates to a data multiplexing device, a program distribution system, a program transmission system, a pay broadcast system, a program transmission method, a conditional access system, and a data reception device and is preferably applied to, for example, a data multiplexing device and a data reception device for a digital broadcast system which performs compression-coding and multiplexing of video data and audio data for transmission.

BACKGROUND ART

Recently, a digital broadcast system has been proposed which uses MPEG2 (Moving Picture Experts Group Phase 2) to compress and encode video data and audio data and then broadcasts encoded streams of data over a ground wave or a satellite wave. This digital broadcast system generates a plurality of transport packets for a plurality of programs each consisting of encoded video streams and encoded audio streams by dividing elementary data such as video data or audio data of each program into a predetermined number of bytes and appending a header to the beginning of each block of divided data. Then these transport packets are multiplexed to broadcast them over a ground wave or a satellite wave.

When a reception device receives transmitted data, that is, multiplexed transport packets, it can obtain the encoded video streams and encoded audio streams of each program by reading out the header information of each transport packets from the received data and restoring the original unmultiplexed elementary data based on the header information.

In such a digital broadcast system, a program generally consists of a plurality of data elements (video data and audio data for a plurality of channels). Therefore, for such a digital broadcast system, it is desirable that an audience should subscribe for each data element contained in a program. For example, suppose that a program consists of a total of four types of data elements, that is, video data, main audio data, subaudio data, and additional data. For a prior digital broadcast system, an audience had to subscribe for each program, that is, all of six data elements. Accordingly, even if a recipient wanted to subscribe only for video data and main audio data, he or she had to subscribe for also unnecessary elements (subaudio and additional data).

Moreover, since a prior scramble device was used before multiplexing, the apparatus must include a scramble device for each program and was unavoidably made large.

In addition, a prior digital broadcast system multiplexed program subscription information and cryptanalytic keys into programs at certain intervals and then transmitted them. Since the highest bit rate of multiplexed streams is limited, the transmission rate may not be sufficiently high for a program due to the transmission of such program subscription information and cryptanalytic keys. Therefore, there was a problem that if a sufficient transmission rate could not be ensured, a transmission buffer for buffering any program data might overflow.

DISCLOSURE OF THE INVENTION

The present invention has been devised in light of the foregoing and proposes a digital broadcast system which allows a recipient to receive only necessary data elements among the data elements constituting a program, that is, which can scramble each data element.

The present invention proposes a digital broadcast system which can minimize the device configuration by avoiding provision of a scramble device for each program.

The present invention proposes a digital broadcast system which can avoid any overflow from a transmission buffer for buffering any program data.

In order to solve such problems, the present invention provides a data multiplexing device which multiplexes and transmits the transport stream packets of program data consisting of a plurality of data elements constructed in the form of transport stream packets. The data multiplexing device comprises a scramble key generation means for generating a scramble key corresponding to a data element and a scramble means for scrambling the corresponding transport stream packet of data element by using a scramble key generated by the scramble key generation means, so that the data multiplexing device may generate a scramble key corresponding to one or more data elements among the plurality of data elements constituting a program and scramble each data element.

By scrambling each data element, an audience can subscribe for each data element.

The present invention provides a program distribution system for distributing a program consisting of a plurality of data elements, which not only manages subscribers' subscriptions for each program or data element through a subscriber management system but generates for each data element a scramble key used for descrambling the data elements contained in the program and based on the generated scramble key, selectively scrambles each data element with respect to encoded data elements contained in a multiplexed stream, so that an audience can subscribe for each data element.

The present invention provides a program transmitting system for transmission a program consisting of a plurality of data elements, which in order for a subscriber to watch and/or hear only programs and data elements for which the subscriber has subscribed, generates a plurality of scramble keys used for scrambling the plurality of data elements contained in the program, selectively scrambles each data element based on the generated scramble key, and multiplexes the scrambled data elements for transmission, so that an audience can subscribe for each data element and descramble only thus subscribed data elements to watch and/or hear them.

The present invention provides a pay broadcast system for broadcasting a program consisting of a plurality of data elements, which not only manages subscribers' subscriptions for each program or data element through a subscriber management system but generates for each data element a scramble key used for descrambling the data elements contained in the program and based on the generated scramble key, selectively scrambles each data element with respect to encoded data elements contained in a multiplexed stream, so that an audience can subscribe for each data element.

The present invention provides a conditional access system for providing a conditional access to only subscribed programs or data elements among a plurality of programs distributed by a program distribution system or a plurality of data elements constituting the programs, which, from a plurality of transport stream packets containing a plurality of encryption scramble keys, filters any transport stream packet containing an encryption scramble key associated with a program or data element subscribed for by a recipient, deciphers the plurality of encryption scramble keys contained in the plurality of filtered transport stream packets, generates a plurality of deciphered scramble keys, and descrambles each data element by using a plurality of deciphered scramble keys corresponding to a plurality of data elements, so that an audience can subscribe for each data element and descramble only thus subscribed data elements to watch and/or hear them.

According to the present invention, by scrambling each multiplexed transport stream packet with the respectively corresponding scramble key, the circuit configuration for scrambling can be made simpler than that for scrambling each transport stream packet before multiplexing.

The present invention comprises a plurality of buffer memories which store a plurality of data packets constituting a plurality of data elements, a multiplexing means which has a switch means for switching the buffer memories and which time-division multiplexes a plurality of packet data strings to provide an output by sequentially time-division switching the buffer memories with the switch means, and a switch control means which selects, according to an input rate for the packet data strings, the plurality of buffer memories switchable by the switch means. Accordingly, any overflow from a buffer memory for buffering higher priority data elements can be avoided by switchably controlling the switch means to exclude a buffer memory for buffering lower priority information among the plurality of buffer memories, when the input rate is higher than a reference rate.

The present invention provides a data reception device for receiving multiplexed data obtained by multiplexing the transport stream packets of program data consisting of a plurality of data elements constructed in the form of transport stream packets, which comprises a scramble key extract means for extracting from the multiplexed data a scramble key corresponding to each data element and a descramble means for descrambling the transport stream packet for each data element contained in the multiplexed data by using a scramble key extracted by the scramble key extract means, so that each data element can be descrambled separately by descrambling the transport stream packet for each data element corresponding to a scramble key by using the scramble key.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a digital broadcast system according to the present invention;

FIG. 2 is a schematic diagram showing the correspondence between elementary data contained in each program and scramble keys;

FIG. 3 is a schematic diagram showing the correspondence between information to be recorded in transport stream packets and their PID values;

FIG. 4 is a schematic diagram showing the correspondence between transport packet types and their PID values;

FIG. 5 is a block diagram showing the configuration of an encoding system;

FIG. 6 is a schematic diagram showing the syntax for a transport packet;

FIG. 7 is a schematic diagram showing the syntax for a transport packet;

FIG. 8 is a schematic diagram showing the syntax for a transport packet;

FIG. 9 is a schematic diagram showing the syntax for a transport packet;

FIG. 10 is a block diagram showing the configuration of a multiplexer system;

FIG. 11 is a schematic diagram showing the correspondence between each table and its PID;

FIG. 12 is a schematic diagram showing the syntax for a program association section;

FIG. 13 is a schematic diagram showing the syntax for a program association section;

FIG. 14 is a schematic diagram showing the correspondence between each section and its PID value;

FIG. 15 is a schematic diagram showing the syntax for a program map section;

FIG. 16 is a schematic diagram showing the syntax for a program map section;

FIG. 17 is a schematic diagram showing the syntax for a conditional access section;

FIG. 18 is a schematic diagram showing the syntax for a conditional access section;

FIG. 19 is a schematic diagram showing the syntax for a conditional access descriptor;

FIG. 20 is a schematic diagram showing the PIDs of elementary data expressed by each table and the contents of the descriptors;

FIG. 21 is a schematic diagram showing the data configuration for EMM packets;

FIG. 22 is a schematic diagram showing the data configuration for ECM packets; and

FIG. 23 is a block diagram showing the configuration of a reception device.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, an embodiment of the present invention is described below with reference to the drawings.

Referring toFIG. 1, a data broadcast system to which a data multiplexing device according to the present invention is applied, is described.

This data broadcast system is a system used for a pay broadcast system such as a satellite digital broadcast system or a ground wave digital broadcast system and as shown inFIG. 1, comprises a broadcast data processing system BDPS (Broadcast_—Data_—Processing_—System)1, a subscriber management system SMS (Subscriber_—Management_—System)2, a subscriber authorization system SAS (Subscriber_—Authorization_—System)3, an EPG (Electronic_—Program_—Guide)system4, aserver system5, arouting system6, anencoding system7, amultiplexer system8, an encoder/multiplexer control unit9, and amodulation circuit10.

The broadcastdata processing system1 is a system for controlling all systems and devices provided within a broadcast station such as thesubscriber management system2, thesubscriber authorization system3, theEPG system4, theserver system5, therouting system6, theencoding system7, themultiplexer system8, the encoder/multiplexer control unit9, and themodulation circuit10. This broadcastdata processing system1 has program planning tables registered with itself, which are used for managing air times for every material including program and promotion materials supplied by program suppliers and program and CM materials produced by the station itself. The broadcastdata processing system1 controls each device and system according to the program planning tables. Such a program planning table consists of a service information file which contains information for program suppliers, an event information file which contains program schedules recorded on a one-hour or one-day basis, and an operation information file which contains program time schedules recorded on a 15-sec basis.

Thesubscriber management system2 is a system used for managing subscriber management information such as subscriber registration information and tolling information. Specifically, thesubscriber management system2 is a core system in a pay broadcast system, which has major functions such as subscription, accounting, and billing. In addition, thesubscriber management system2 has another function for managing information on keys such as a scramble key Ks for scrambling a data element and a work key Kw for enciphering such a scramble key Ks as well as information on broadcast contractors, program suppliers, and programming agencies. Thesubscriber management system2 has still another function for processing, in real time, audience information supplied by an IRD provided at the receiving end through a telephone line. Thesubscriber management system2 eventually provides to thesubscriber authorization system3 described later, some EMM (Entitlement_—Management_—Message) data which contains information on subscription as well as a work key Kw. Such EMM data will be described later in detail.

Thesubscriber authorization system3 generates an enciphered work key Kw′ by enciphering a work key Kw contained in the EMM data received from thesubscriber management system2 through a predetermined encryption algorithm using a master key Km. It should be appreciated that an encryption algorithm used for a digital broadcast system according to the present invention is an encryption algorithm called CRYPS (a trademark of SONY) developed by the present applicant, which adopts a block encryption technique similar to the DES system established by the Department of Commerce. Thesubscriber authorization system3 replaces a work key Kw contained in the EMM data supplied by thesubscriber management system2 with a work key Kw′ enciphered through the encryption algorithm CRYPS and then generates thus enciphered EMM data. In order to transmit such EMM data enciphered through the present applicant's unique encryption algorithm via satellites, thesubscriber authorization system3 translates the enciphered EMM data into transport stream packets by inserting the enciphered EMM data in the payload section of a transport stream packet. In the following description, a transport stream packet containing such EMM data will be referred to as an EMM packet. It should be also appreciated that thesubscriber authorization system3 receives a PID (packet identifier) given to such an EMM packet from the encoder/multiplexer control unit9 described later over a network.

Thesubscriber authorization system3 has a work key table in which 256 work keys (Kw) are associated with work key identification numbers (Kw_—No) for identifying these work keys and this work key table can be downloaded into memory of themultiplexer system8 over a network. The reason why such a work key table is downloaded into themultiplexer system8 is that themultiplexer system8 obtains an unenciphered work key Kw from the work key identification numbers (Kw_—No) because only enciphered work keys Kw′ are transmitted by thesubscriber authorization system3 to themultiplexer system8.

Moreover, thesubscriber authorization system3 generates a scramble key Ks to scramble each data element contained in a transmitted program. In this regard, thesubscriber authorization system3 generates a different scramble key Ks for each program or for each data element contained therein. For example, as shown inFIG. 2, a scramble key Ks1 is generated for scrambling the video data and main audio data constituting the first program, respectively, a scramble key Ks2 is generated for scrambling the video data and main audio data constituting the second program, a scramble key Ks3 is generated for scrambling the subaudio data of the second program, and a scramble key Ks4 is generated for scrambling the private data of the second program. Which scramble key is assigned to which element of which program can be determined by thesubscriber authorization system3 arbitrarily, depending on the content of the program. For example, as with the fourth program, different scramble keys Ks7 through Ks10 can be assigned to the video data, main audio data, subaudio data, and private data, respectively, or as with the fifth program, the same scramble key Ks11 can be assigned to all the video data, main audio data, subaudio data, and private data.

Moreover, in order to enhance the security level of the encryption/decryption system used for the digital broadcast system, thesubscriber authorization system3 updates these scramble keys Ks1 through Ks19 at intervals of 4 seconds with a random number generator within thesubscriber authorization system3.

In addition, thesubscriber authorization system3 generates a plurality of ECM (Entitlement_—Control_—Message) data items used for descrambling. This ECM data consists of a work key number for specifying at least a work key Kw listed in the work key table, a scramble key Ks for scrambling data streams, and a CA_—system_—ID for identifying thesubscriber authorization system3. Therefore, in the example where 19 scramble keys Ks1 through Ks19 are used as shown inFIG. 2, thesubscriber authorization system3 generates 19 ECM data items, because only a scramble key is registered with an ECM data item.

In order to transmit such a plurality of generated ECM data items, thesubscriber authorization system3 further translates the plurality of ECM data items into transport stream packets by inserting the plurality of ECM data items in the payload section of a transport stream packet. In the following description, a transport stream packet containing such ECM data will be referred to as an ECM packet. InFIG. 1, the term ECM1 shows an ECM packet containing the scramble key Ks1, the term ECM2 shows an ECM packet containing the scramble key Ks2, and similarly, the terms ECM3 through ECM19 show ECM packets containing the scramble keys Ks3 through Ks19, respectively. It should be also appreciated that thesubscriber authorization system3 receives a PID (packet identifier) given to each of the plurality of ECM packets from the encoder/multiplexer control unit9 described later over a network. It should be further appreciated that inFIG. 1, the ECM packets are shown to be supplied directly to the multiplexer system but this is only for the sake of clarity and in fact the ECM packets will be supplied to themultiplexer system8 via a network and the encoder/multiplexer control unit9.

Now, why the above-mentioned work keys and scramble keys are to be used for the digital broadcast system is described below.

A typical digital broadcast system generally uses a pay broadcast system which authorizes only subscribers to watch and/or hear the programs and sends accounts to those subscribers based on their subscription conditions. To accomplish a pay broadcast system, such a digital broadcast system must scramble programs with scramble keys generated by the broadcast station before transmission and allow only subscribers to descramble the programs to watch and/or hear them. Specifically, in order to allow only subscribers to descramble such scrambled data elements at the receiver end, scramble keys Ks used in scrambling must be used also for descrambling. To automatically descramble programs transmitted via satellites, these scramble keys Ks must be transmitted to the receiver end.

However, if these scramble keys Ks are to be transmitted to the receiver end, an unauthorized recipient may be able to obtain these scramble keys Ks and consequently to watch and/or hear all transmitted programs free of charge. Therefore, at the first level of security, the pay broadcast system according to the present invention changes these scramble keys Ks at intervals of several seconds with a random number generator and enciphers these scramble keys Ks with work keys Kw. The encryption of scramble keys Ks with a random number generator can be accomplished by software and therefore, can provide a much higher level of security for the encryption technique.

To further enhance the security level of a conditional access system, the digital broadcast system according to the present invention enciphers these scramble keys Ks by using work keys Kw in anencryption circuit822 of themultiplexer system8 which is described later and then transmits enciphered scramble keys Ks′ to the receiver end. That is, the security level can be enhanced to the utmost by transmitting enciphered scramble keys Ks rather than by transmitting the scramble keys Ks themselves used in scrambling programs. At the receiver end, a decrypter for deciphering the enciphered scramble keys Ks′ is provided in a security module (IC card) in the receiver and all decryption operations are performed in the security module. The security module composed of an IC card has such a structure that the program code contained therein cannot be decoded in effect and therefore, it may be quite difficult for an outsider to decipher the scramble keys.

TheEPG system4 is a system to create program guide data associated with transmitted programs. Program guide data (EGP data) refers to, for example, data for informing air times of programs to be broadcasted in future, character data for explaining the contents of selected programs, and title data for programs. The EPG data may be created mainly by the broadcast station or a program supplier may create special EPG data for its own programs.

Theserver system5 consists of a server constructed by connecting disk drives containing various materials into an array and a server control computer for controlling the recording/playback operations of the server. Theserver system5 is connected to the broadcastdata processing system1 through the LAN in the broadcast station such as Ethernet, so that it can be controlled to transmit programs according to a program planning list of the program data processing system. Theserver system5 has several server functions corresponding to the types of materials recorded therein, such as a CM server function for supplying CM materials, a daily server function for supplying television program materials and news program materials, and a video-on-demand (VOD) server function for supplying television program materials and movie materials, and can provide a plurality of desired programs over a certain channel under the control of the broadcastdata processing system1.

Therouting system6 is a system for routing multichannel data supplied by theserver system5 to appropriate channels. Therouting system6 is connected to the broadcastdata processing system1 through Ethernet, so that it can be controlled to transmit programs over appropriate channels according to a program planning list of the program data processing system.

The encoder/multiplexer control unit9 supplies control commands to control theencoding system7 and themultiplexer system8 to theencoding system7 and themultiplexer system8 via a network. The encoder/multiplexer control unit9 receives an EPG packet from theEPG system4 via the network as well as ECM packets (ECM1 through ECM19) and an EMM′ packet from thesubscriber authorization system3 via the network and then supplies the received EPG, EMM′, and ECM packets to themultiplexer system8. In addition, the encoder/multiplexer control unit9 supplies private data to theencoding system7 as well as program specific information (PSI: Program_—Specific_—Information) to themultiplexer8.

Program specific information PSI consists of a program association table (PAT: Program_—Association_—Table) for showing a specified program number and its corresponding transport stream packet in a program map table (PMT), a program map table (PMT: Program_—Map_—Table) for showing a transport stream packet in which data elements for the specified program are described, and a conditional access table (CAT: Conditional_—Access_—Table) for specifying a transport stream packet containing EMM data. The encoder/multiplexer control unit9 generates a program association table PAT, a program map table PMT, and a conditional access table CAT and provides these generated tables in the form of a transport stream. In the following description, a transport stream packet containing such a program association table PAT will be referred to as a PAT packet, a transport stream packet containing such a program map table PMT will be referred to as a PMT packet, and a transport stream packet containing such a conditional access table CAT will be referred to as a CAT packet.

In order to assign appropriate packet identifiers PID to transport stream packets created by theEPG system4, thesubscriber authorization system3, and theencoding system7, the encoder/multiplexer control unit9 generates the appropriate packet identifiers PID and supplies them to thesubscriber authorization system3, theEPG system4, and theencoding system7.

A packet identifier (PID: Packet Identification) is an identifier for identifying a transport stream packet. Such a packet identifier PID is unique data of 13 bits determined according to the type of data stored in the payload of a transport stream packet. For example, as shown inFIG. 3, a PID value of “0x0000” is specified for a transport stream packet which stores information on a program association table PAT in its payload, and a PID value of “0x0001” is specified for a transport stream packet which stores information on a conditional access table CAT in its payload. One of the PID values “0x0020” through “0x1FFE” is selected as a PID value for a transport stream packet which stores information on a program map table PMT or elementary data such as video data and audio data in its payload.

When generating a PID to be assigned to each transport stream packet, the encoder/multiplexer control unit9 generates a PID table showing the correspondence between PIDs specified for transport stream packets and scramble keys Ks used for scrambling. The PID table is a table for storing the previously used PID values and by referring to the PID values stored in the PID table, the encoder/multiplexer control unit9 can determine whether a PID value has been used previously and generate a new PID value which is not a duplicate of any previous PID value. The PID table is used also for determining whether a multiplexed transport stream packet should be scrambled.

For example, as shown inFIG. 4, the PID table shows the correspondence between PIDs specified for generated transport stream packets and scramble keys Ks used for data stored in the corresponding transport stream packets. InFIG. 4, a PID value for PAT packets is fixed to “0x0000”, a PID value specified for PMT packets corresponding to the first program is “0x0100”, a PID value specified for PMT packets corresponding to the second program is “0x0101”, a PID value specified for ECM packets with a scramble key Ks1 for scrambling Video[1] packets used for video data of the first program and Main_—Audio[1] packets used for main audio data is “0x0300”, a PID value specified for ECM packets with a scramble key Ks2 for scrambling Video[2] packets used for video data of the second program is “0x0301”, a PID value specified for ECM packets with a scramble key Ks2 for scrambling Main_—Audio[2] packets used for main audio data of the second program is “0x0302”, a PID value specified for ECM packets with a scramble key Ks3 for scrambling Sub_—Audio[2] packets used for subaudio data of the second program is “0x0303”, and a PID value specified for ECM packets with a scramble key Ks4 for scrambling Private[2] packets used for private data of the second program is “0x0304”. A PID value specified for Video[1] packets used for video data of the first program is “0x0500” and this type of packets are scrambled with a scramble key Ks1. A PID value specified for Main_—Audio[1] packets used for main audio data of the first program is “0x0501” and this type of packets are scrambled with a scramble key Ks1. A PID value specified for Video[2] packets used for video data of the second program is “0x0502” and this type of packets are scrambled with a scramble key Ks2. A PID value specified for CAT packets is fixed to “0x0001” and a PID value specified for EMM packets is “0x700”.

As shown inFIG. 5, theencoding system7 comprises a plurality ofMPEG video encoders711V through719V for encoding video data supplied over a plurality of channels according to the MPEG2 standard,MPEG audio encoders711A through719A for encoding a plurality of audio data streams corresponding to the video data streams according to the MPEG2 standard, multiplexingcircuits721 through729 for multiplexing streams supplied by each video encoder and each audio encoder and private data streams supplied by the encoder/multiplexer control unit9, and anencoding controller70 for controlling the video/audio encoders711 through719 and the multiplexingcircuits721 through729. It should be appreciated that the encoding system as shown inFIG. 5 is configured to encode programs for 9 channels but, of course, it may handle not only 9 channels but any number of channels.

Each of thevideo encoders711V through719V generates encoded bit streams by encoding video data according to the MPEG2 standard. Then the video encoder generates PES (Packetized Elementary Stream) packets by dividing an encoded bit stream in picture units and appending a header to the divided bit stream. Next, the video encoder generates transport stream packets by dividing a PES packet in 184 bytes and appending a header of 4 bytes to the divided bit stream of 184 bytes. Data consisting of transport stream packets arranged in a stream is called a transport stream. In generating transport stream packets, the encoder/multiplexer control unit9 supplies to each of thevideo encoders711V through719V a packet identifier (PID) for identifying a transport stream packet containing the encoded video data.

Each of theaudio encoders711A through719A generates encoded bit streams by encoding main audio data and subaudio data according to the MPEG2 standard. Like the video encoders, each of theaudio encoders711A through719A generates PES packets from the bit streams and then generates transport stream packets containing audio data by dividing a PES packet in 184 bytes and appending a header of 4 bytes. In generating transport stream packets, the encoder/multiplexer control unit9 supplies to each of theaudio encoders711A through719A a packet identifier (PID) for identifying a transport stream packet containing the encoded audio data.

Each of the multiplexingcircuits721 through729 generates a transport stream by multiplexing a transport stream containing encoded video data, a transport stream containing encoded audio data, and a transport stream containing private data. Specifically, the multiplexing circuit multiplexes these streams by switching between the transport stream containing encoded video data, the transport stream containing encoded audio data, and the transport stream containing private data in units of transport stream packets. Therefore, in an output transport stream, transport stream packets containing encoded video data, transport stream packets containing encoded audio data, and transport stream packets containing private data are intermingled. In this regard, private data is placed in a transport stream packet by the encodingcontroller70 and then supplied to each of the multiplexing circuits through a network.

The encodingcontroller70 specifies an appropriate encoding bit rate for each of the video and audio encoders. For example, the encodingcontroller70 assigns a higher bit rate to an encoder for encoding a program such as sports which requires more encoded bits and assigns a lower bit rate to an encoder for encoding a program such as news which may generate fewer encoded bits. That is, it grasps a complexity (which is used as an index of how many bits are generated by encoding) of video data for each channel relative to the other channels and then assigns the highest bit rate to a channel for video data of the highest complexity and assigns other lower bit rates in descending order. Of course, any assigned bit rate is not program-specific and may be changed depending on the complexity of video data in that program.

Next, the structure and syntax for this transport stream packet are described below in detail with reference toFIGS. 6 through 9.

A transport stream packet consists of a header of 4 bytes and a payload section of 184 bytes for storing various types of data and data elements.

The header of a transport stream packet consists of the following fields: sync_—byte, transport_—error_—indicator, payload_—unit_—start_—indicator, transport_—priority_—PID, transport_—scrambling_—control, adaptation_—field_—control, continuity_—counter, and adaptation_—field.

The sync_—byte field is a field having a fixed length of 8 bits and detects a synchronous pattern in the bit stream. This field is defined to have a fixed value of “01000111” (0X47) and can detect a synchronous condition by detecting this bit pattern in the stream.

The transport_—error_—indicator field is a flag of 1 bit and when set to “1”, indicates that an uncorrectable error of at least 1 bit exists in the transport stream packet.

The payload_—unit_—start_—indicator field is a flag of 1 bit and has a meaning significant to transport stream packets which carry video/audio data and other elementary data or program specific information (PSI). If the payload section of a transport stream packet contains elementary data, the payload_—unit_—start_—indicator field has the following meaning: when the payload_—unit_—start_—indicator field is “1”, it indicates that elementary data is inserted at the beginning of the payload section of this transport stream packet; when the payload_—unit_—start_—indicator field is “0”, it indicates that elementary data is not inserted at the beginning of the payload section of this transport stream packet. If the payload_—unit_—start_—indicator field is set to “1”, it indicates that only one PES packet starts at a certain transport stream packet. On the contrary, if the payload section of a transport stream packet contains PSI data, the payload_—unit_—start_—indicator field has the following meaning: when the transport packet carries the first byte of the PSI section, the payload_—unit_—start_—indicator field is “1”; when the transport stream packet does not carry the first byte of the PSI section, the payload_—unit_—start_—indicator field is “0”. If the transport stream packet is a null packet, the payload_—unit_—start_—indicator field is also “0”.

The transport_—priority field is an identifier of 1 bit for indicating the priority of a transport packet. When the transport_—priority field is set to “1”, this transport packet is a packet having the same packet identifier PID, which indicates that this packet has a higher priority than that having the transport_—priority field set to a value other than “1”. For example, a certain packet in an elementary stream can be assigned a priority by setting a packet identifier of the transport_—priority field.

The transport_—scrambling_—control field is data of 2 bits for indicating the scrambling mode of the transport stream packet payload. The scrambling mode indicates whether data stored in the payload has been scrambled and the type of scramble. It is required by the standard that the transport stream packet header and the adaptation field should not be scrambled with a scramble key Ks. Therefore, by using this transport_—scrambling_—control field, it can be determined whether data stored in the transport stream random_—access_—indicator, elementary_—stream_—priority_—indicator, PCR_—flag, OPCR_—flag; splicing_—point_—flag, splicing_—point, transport_—private_—data_—flag, adaptation_—field_—extension_—flag, program_—clock_—reference (PCR), original_—program_—clock_—reference (OPCR), splice_—countdown, transport_—private_—data_—length, private_—data, adaptation_—field_—extension_—length, ltw_—flag (legal_—time_—window flag), piecewise_—rate_—flag, and seamless_—splice_—flag.

The adaptation_—field_—length field is data indicating the number of bytes of an adaptation field following this adaptation_—field_—length field. If the adaptation_—field_—control field is “11”, the adaptation_—field_—length is 0 through 182 bits; if the adaptation_—field_—control is “10”, the adaptation_—field_—length is 183 bits. It should be appreciated that stuffing is required to fill in with some bits when elementary streams are not enough to fill in the payload of a transport stream.

The discontinuity_—counter field is data indicating whether a system clock reference (SCR) is reset in the middle of a plurality of packets with the same PID to be discontinuous. If the system clock reference is discontinuous, this discontinuity_—counter field is “1”; if the system clock reference is still continuous, this discontinuity_—counter field is “0”. It should be appreciated that the system clock reference is reference information which an MPEG decoder for decoding video and audio data uses to set a system time clock for the decoder to a timing value intended by the encoder.

The random_—access_—indicator field is data indicating the beginning of a video sequence header or an audio frame. That is, this random_—access_—indicator field is data indicating an access point (which is the beginning of a frame) for video or audio data when data elements are accessed randomly.

The elementary_—stream priority_—indicator field is data indicating the priority of elementary stream data carried in the payload of this transport stream packet in packets with the same PID. For example, when video data of an elementary stream is intra-coded, the elementary_—stream_—priority_—indicator field is set to “1”. On the contrary, the elementary_—stream_—priority_—indicator of a transport stream containing inter-coded video data is set to “0”.

The PCR_—flag field is data indicating whether PCR (program_—clock_—reference) data exists in an adaptation field. If PCR data exists in the adaptation field, the PCR_—flag field is set to “1”; if no PCR data exists, the PCR_—flag field is set to “0”. It should be appreciated that the PCR data is used by a decoder at the receiver end to obtain a proper timing of a decoding operation for decoding transmitted data.

The OPCR_—flag field is data indicating whether OPCR (original_—program_—clock_—reference) data exists in an adaptation field. If OPCR data exists in the adaptation field, the OPCR_—flag field is set to “1”; if no OPCR data exists, the OPCR_—flag field is set to “0”. It should be appreciated that the OPCR data is used by a splicing operation to reconstruct a transport stream from a plurality of original transport streams and indicates PCR data for an original transport stream.

The splicing_—point_—flag field is data indicating whether splice_—countdown data exists in an adaptation field to show an edit point (splice point) at the transport level. If splice_—countdown data exists in the adaptation field, the splicing_—point_—flag field is “1”; if no splice_—countdown data exists in the adaptation field, the splicing_—point_—flag field is “0”.

The transport_—private_—data_—flag field is data indicating whether private data used to describe certain user data exists in an adaptation field. If private data exists in the adaptation field, the transport_—private_—data_—flag field is set to “1”; if no private data exists in the adaptation field, the transport_—private_—data_—flag field is set to “0”.

The adaptation_—field_—extension_—flag field is data indicating whether an extension field exists in an adaptation field. If an extension field exists in the adaptation field, the adaptation_—field_—extension_—flag field is set to “1”; if no extension field exists in the adaptation field, the adaptation_—field_—extension_—flag field is set to “0”.

The program_—clock_—reference (PCR) is a reference clock to be referenced when the clock at the receiver end is made in phase with the clock at the transmitting end. This PCR data contains time data when each transport packet is generated. The PCR data is 42 bits long, consisting of program_—clock_—reference_—base of 33 bits and program_—clock_—reference_—extension of 9 bits. 24 hours can be counted by counting the system clock in the range of 0 through 299 with the program_—clock_—reference_—extension and adding a bit to the program_—clock_—referece_—base with a carry generated when the count 299 is reset to 0.

The original_—program_—clock_—reference (OPCR) field is data used to reconstruct a single program transport stream from certain transport streams. When such a single program transport stream is completely reconstructed, the original_—program_—clock_—reference is copied into the program_—clock_—reference field.

The splice_—countdown field is data indicating the number of packets necessary to reach an editable (spliceable) point at the transport stream packet level in transport stream packets with the same PID. Therefore, a transport stream packet at an editable splicing point has the splice_—countdown field set to “0”. In a transport packet with the splice_—countdown field set to “0”, the last byte of the transport stream packet payload can be spliced by relocating it to the last byte of an encoded picture.

In this regard, a splicing operation is performed to concatenate two different elementary streams at the transport level to form a new transport stream. Splicing operations can be divided into two types: a seamless splice with no discontinuity of decoding and a nonseamless splice with a discontinuity of decoding. The case where no discontinuity of decoding occurs means that the decoding time for an access unit of a newly added stream is consistent with the decoding time for an access unit of an old stream before splicing. On the contrary, the case where a discontinuity of decoding occurs means that the decoding time for an access unit of a newly added stream is inconsistent with the decoding time for an access unit of an old stream before splicing.

The transport_—private_—data_—length field is data indicating the number of bytes of private data in an adaptation field.

The private_—data is a field which is not required specifically by the standard but can be used to describe certain user data in an adaptation field.

The adaptation_—field_—extension_—length field is data indicating the length of adaptation field extension data in an adaptation field.

The ltw_—flag (legal_—time_—window_—flag) field is data indicating whether ltw_—offset data showing an offset value of the display window exists in an adaptation field.

The piecewise_—rate_—flag field is data indicating whether piecewise_—rate data exists in an adaptation field.

The seamless_—splice_—flag field is data indicating whether the splicing point is a normal splicing point or a seamless splicing point. When the seamless_—splice_—flag field is “0”, it indicates that the splicing point is a normal splicing point; when the seamless_—splice_—flag field is “1”, it indicates that the splicing point is a seamless splicing point. A normal splicing point means that the splicing point exists at a break in PES packets and that the splicing packet immediately preceding this splicing point ends at the access unit and the next transport packet with the same PID begins at the header of a PES packet. On the contrary, a seamless splicing point means that a splicing point exists in the middle of a PES packet and that in order for the decoding time for an access unit of a newly added stream to be consistent with the decoding time for an access unit of an old stream before splicing, the characteristics of the old stream are partly used as those of the new stream.

Next, themultiplexer system8 is described below in detail with reference toFIG. 10. Themultiplexer system8 is a system which multiplexes a PAT packet, a PMT packet, a CAT packet, transport stream packets containing encoded elementary data, an EPG packet, ECM packets, and an EMM′ packet to generate a transport stream.

Specifically, themultiplexer system8 comprises amultiplexer controller81 for controlling all circuits within themultiplexer system8, anencryption block82 for enciphering ECM packets supplied by thesubscriber authorization system3, FIFO buffers841 through843 for buffering PAT packets, PMT packets, and CAT packets supplied by the encoder/multiplexer system9 as program specific information PSI, respectively, FIFO buffers851 through859 for buffering transport stream packets containing a plurality of programs, respectively, FIFO buffers861 through863 for buffering ECM packets, EMM packets, and EPG packets, respectively, anFIFO controller83 for controlling the read/write operations of each FIFO buffer as well as for monitoring free area of each FIFO buffer, amultiplexing circuit87 for multiplexing transport stream packets supplied by the FIFO buffers to generate a multiplexed transport stream, and ascramble block88 for scrambling data elements contained in a multiplexed transport stream packet.

Themultiplexer controller81 receives an EPG packet, an EMM′ packet, ECM packets (ECM1 through ECM19), a PAT packet, a PMT packet, and a CAT packet from the encoder/multiplexer control unit9 and supplies each packet to an appropriate circuit. Themultiplexer controller81 receives also a PID table from the encoder/multiplexer control unit9 and supplies it to thescramble block88.

Theencryption block82 is a block for enciphering scramble keys Ks contained in a plurality of ECM packets supplied by thesubscriber authorization system3 through the encoder/multiplexer control unit9 and themultiplexer controller81. Theencryption block82 has aRAM821 for storing a work key table downloaded from thesubscriber authorization system3 before the encryption operation and anencrypter822 for enciphering the scramble keys Ks contained in the ECMs based on work keys Kw.

Now, the encryption operation of theencryption block82 is described below by explaining, by way of example, the case where a scramble key Ks1 for scrambling elementary data constituting the first program is to be enciphered. First, a work key number Kw_—No contained in an ECM packet ECM1 is supplied to theRAM821. TheRAM821 stores a work key table downloaded from the subscriber authorization system, which shows the correspondence between work key numbers Kw_—No and work keys Kw. Since the work key number Kw_—No contained in the packet ECM1 is supplied to theRAM821, a work key Kw corresponding to the supplied work key number Kw_—No is provided by theRAM821. Theencryption circuit822 receives an ECM packet containing a scramble key Ks1 and also receives a work key Kw from theRAM821. Theencryption circuit822 enciphers the scramble key Ks1 contained in the source ECM with the work key Kw and then generates an enciphered scramble key Ks1′. Theencryption circuit822 accumulates the enciphered scramble key Ks1′ rather than the unenciphered scramble key Ks in the source ECM and provides as an enciphered ECM packet a transport stream packet containing the enciphered scramble key Ks1′. It should be appreciated that the encryption algorithm is the same as that used at thesubscriber authorization system3 for enciphering work keys Kw contained in EMM data, that is, the encryption algorithm CRYSP.

Theencryption block82 supplies to the scramble block88 a scramble key Ks1 which is supplied as ECM data. It should be appreciated that the scramble key Ks1 to be supplied to thescramble block88 has not been enciphered with a work key Kw.

In the foregoing example, scramble keys Ks1 accumulated in the first ECM packet ECM are enciphered as described above but the encryption operations for other scramble keys Ks2 through Ks19 are performed identically. Therefore, enciphered ECM packets ECM1′ through ECM19′ are provided by theencryption block82 to theFIFO buffer861 and unenciphered scramble keys Ks1 through Ks19 are also provided by theencryption block82 to thescramble block88.

The multiplexingcircuit87 supplies to thescramble block88 some packets selected from PAT packets, PMT packets, and CAT packets buffered in theFIFO841 through843, transport stream packets containing a plurality ofprograms Program1 throughProgram9 buffered in theFIFO851 through859, and ECM packets, EMM packets, and EPG packets buffered in theFIFO861 through863, depending on the amount of data in each FIFO. In this retard, theFIFO controller83 monitors the input rate for packet data supplied to each FIFO and it notifies themultiplexer controller81 of an excess input rate condition when the sum of all input rates for each FIFO exceeds a predetermined output rate. Thus, themultiplexer controller81 excludes theFIFO862 for buffering EMM packets from the target FIFOs to be selected by the multiplexingcircuit87 and then switches the other FIFOs as a selection target to supply to thescramble block88 packet data from a switched FIFO. Therefore, as the number of FIFOs to be selected by the multiplexingcircuit87 decreases, the number of select operations for a target FIFO increases and thereby the data output rate of each FIFO can be increased correspondingly to the excess input rate condition.

When the sum of all input rates for each FIFO is under a predetermined output rate, themultiplexer controller81 supplies to thescramble block88 EMM packets buffered in theFIFO862 by restoring theFIFO862 as a target FIFO to be selected by the multiplexingcircuit87. It should be appreciated that EMM data indicating the subscription information buffered in theFIFO862 may not be changed frequently and substantially no disadvantageous situations will occur even if that FIFO is temporarily excluded from the target FIFOs to be selected by the multiplexingcircuit87.

When the sum of all input rates for each FIFO further increases to such an extent that only the exclusion of thesingle FIFO862 from the target FIFOs to be selected by the multiplexingcircuit87 cannot deal with such an excess input rate condition, themultiplexer controller81 excludes not only theFIFO862 for buffering EMM data but theFIFO863 for buffering EPG data. Such an additional exclusion can further decrease the number of FIFOs to be selected by the multiplexingcircuit87 and further increase the number of select operations for a target FIFO and thereby the data output rate of each FIFO can be further increased correspondingly to the excess input rate condition. It should be appreciated that EPG data indicating the program guide information buffered in theFIFO863 may not be changed frequently and substantially no disadvantageous situations will occur even if that FIFO is temporarily excluded from the target FIFOs to be selected by the multiplexingcircuit87.

Thescramble block88 has aPID detection circuit881 and ascramble circuit882. ThePID detection circuit881 receives transport stream packets from the multiplexingcircuit87 as well as a PID table (FIG. 4) from the encoder/multiplexer control unit9 through themultiplexer controller81. Since the PID table shows the correspondence between PID values and scramble keys used in generating transport stream packets, thePID detection circuit881 detects a desired scramble key Ks by referencing the PID values stored in the PID table and then supplies the detected scramble key Ks to thescramble circuit882. Thescramble circuit882 uses the scramble key Ks supplied by thePID detection circuit881 to scramble the transport stream packets containing program data associated with this scramble key Ks and provides an output to the modulation circuit10 (FIG. 1).

Now, the program specific information is described below.

Program specific information (PSI: Program_—Specific_—Information) is information indicating which data is contained in which packet among the transport stream packets obtained by multiplexing a plurality of programs and data. Therefore, a decoder can decode desired data by referencing this program specific information.

The program specific information can be classified into 4 table structures as shown inFIG. 11. A program association table (PAT: Program_—Association_—Table) is a table for indicating specified program numbers and their corresponding program map table (PMT) PIDs. A program map table (PMT: Program_—Map_—Table) is a table for indicating PIDs of packets in which elements of a specified program are described. A network information table (NIT: Network_—Information_—Table) is a private table for indicating information which is to be used in transmitting network parameters but is not specifically required by any standard. A conditional access table (CAT: Conditional_—Access_—Table) is a table for assigning unique PIDs to EMM packets. In the following description, the program association table, the program map table, and the conditional access table are described in detail.

First, the program association table is described below with reference toFIGS. 12 and 13.

The program association table PAT is a table used to specify each transmitted program and the PID of a transport stream packet which specifies the content of the program. Specifically, the program association table PAT consists of the following: table_—id, section_—syntax_—indicator, section_—length, transport_—stream_—id, version_—number, current_—next_—indicator, section_—number, last_—section_—number, program_—number, network_—PID, and program_—map_—PID.

The table_—id shows a unique identification number assigned to each table as shown inFIG. 14. The table_—id of the program association table PAT is “0x00”, the table_—id of the conditional access table CAT is “0x01”, and the table_—id of the program map table PMT is “0x02”.

The section_—syntax_—indicator is a constant fixed to “1”.

The section_—length is a field for indicating in bytes the length from the bit following this section_—length to the last byte of the CRC section.

The transport_—stream_—id is identification data for discriminating between this transport stream and other transport streams multiplexed in the network.

The version_—number is data for indicating the version number of the program association table (PAT). The version number is an integer in therange 0 through 31 and incremented by 1 when any setting in the program association table is changed, that is, any characteristic of a transport stream changes. The decoder at the receiver end references the version_—number to determine that only the section of the latest version is valid.

The current_—next_—indicator is data for indicating whether the transmitted program association table is currently available.

The section_—number is data for indicating the program association table section number. For example, the section_—number of the program_—association_—section( ) contained in the program association table is set to “0x00” to show that it is the first section.

The last_—section_—number is data for indicating the section number of the last section among all the sections specified in the program association table. Therefore, the last_—section_—number allows the system to know the number of sections specified in the program association table.

The program_—number is a unique number given to each of a plurality of programs to be multiplexed. For example, in a data transmission device according to the present invention, theprogram numbers 1 through 9 are assigned to 9 programs to be multiplexed, respectively. The program_—number is data which can be defined by the user arbitrarily. However, when the program_—number is set to 0, the program_—number indicates that a network information table (NIT) exists in the stream.

The network_—PID is data for indicating the PID in which a network information table (NIT) in the stream is described. The network information table (NIT) is a table which can be set by the user arbitrarily and is not used for the present device.

The program_—map_—PID is data for indicating the PID of a transport stream packet having a program map table applied to the program specified by the program_—number. For example, if a program consists of a piece of video data and 4 pieces of audio data, a PID which specifies a transport stream packet having the video data of that program and 4 PIDs which specify transport stream packets having the audio data of that program are described in the program association table.

Next, the program map table (PMT) is described below with reference toFIGS. 15 and 16.

The program map table is a table used to show the mapping between program numbers and data elements constituting those programs. That is, the program map table is a section to specify, for each program number, PIDs of transport stream packets to transmit elements such as video data, audio data, and other additional data constituting that program. Specifically, the program map table consists of the following: table_—id, section_—syntax_—indicator, section_—length, program_—number, version_—number, current_—next_—indicator, section_—number, last_—section_—number, PCR_—PID, program_—info_—length, descriptor( ), stream_—type, elementary_—PID, ES_—info_—length, and descriptor( ).

The table_—id shows a unique identification number assigned to identify each table. The table_—id of the program map table is “0x02”.

The section_—syntax_—indicator is a constant fixed to “1”.

The section_—length is a field for indicating in bytes the length from the bit following this section_—length to the last byte of the CRC section.

The program_—number is a unique number given to each of a plurality of programs to be multiplexed. For example, in a data transmission device according to the present invention, theprogram numbers 1 through 9 are assigned to 9 programs to be multiplexed, respectively.

The version_—number is data for indicating the version number of a program map section which constitutes the program map table. The version number is incremented when data transmitted in the program map section is changed.

The current_—next_—indicator is data for indicating whether the transmitted program association table is currently available. If the program association table is currently available, the current_—next_—indicator is set to “1”; if the program association table is not currently available, the current_—next_—indicator is set to “0”.

The section_—number is data for indicating the number of a section contained in the program map table and it is always set to “0x00” because only one program map section exists to constitute the program map table.

The last_—section_—number is data for indicating the section number of the last section among all the sections specified in the program map table. Therefore, the last_—section_—number is always set to “0x00” in the program map section which constitutes the program map table.

The PCR_—PID is data for indicating the PID of a transport packet containing PCR data which is valid for a program specified by the program_—number.

The program_—info_—length is data for specifying the number of bytes for the descriptor( ) described following the program_—info_—length field.

The descriptor( ) is a data structure used to expand the definitions of programs and program elements. Various descriptors may be possible, for example, video_—stream_—descriptor( ) to describe basic information which identifies encoding parameters for video elementary streams; audio_—stream_—descriptor( ) to describe basic information which identifies an encoding version for audio elementary streams; hierarchy_—descriptor( ) to describe information which identifies program elements containing hierarchically-encoded video and audio data multiplexed into a plurality of streams; resistration_—descriptor( ) to describe information which identifies private data uniquely and definitely; data_—stream_—alignment_—descriptor( ) to describe the alignment type which exists between elementary streams associated with each other; target_—background_—descriptor to describe information which specifies a background window to be displayed in the background of the display window for transmitted video data; video_—window_—descriptor to describe information which specifies the display position of the display window for transmitted video data; CA_—descriptor( ) to describe a subscription information EMM, a program decryption information ECM, and other data; language_—descriptor( ) to describe information which identifies a language and the language used by associated program elements; system_—clock_—descriptor( ) to transmit information for the system clock used for generation of time stamps; multiplex_—buffer_—utilization_—descriptor( ) to describe data which indicates the critical levels of underflow and overflow of data occupancy in the STD (system_—target_—decoder) multiplex buffer containing the video_—buffer_—verifier; copyright_—descriptor( ) to describe information which allows identification of audio/visual works to protect the copyrights thereof; maximum_—bitrate_—descriptor( ) to describe information which specifies the maximum bit rate for transmitted data elements; private_—data_—indicator_—descriptor( ) to specify transmission of private data; smoothing_—buffer_—descriptor( ) to describe information for the size of a smoothing buffer and the leak rate of output from that buffer; STD_—descriptor( ) to specify the leak value of an STD buffer; and ibp_—descriptor( ) to describe information for encoding types.

It should be appreciated that in a data transmission device according to the present invention, a data structure of descriptor( ) used in the program map table is intended to describe information which specifies the PID of a transport stream packet containing a program decryption information ECM.

The stream_—type is data for specifying the type of a program element contained in a packet with the PID specified by the elementary_—PID described below. For example, the stream_—type is set to “0x01” if a program element contained in the packet is video data conformable to the ISO/IEC11172 standard, it is set to “00x02” if a program element is video data conformable to the ISO/IEC13818-2 standard, it is set to “0x03” if a program element is audio data conformable to the ISO/IEC11172 standard, and it is set to “0x04” if a program element is audio data conformable to the ISO/IEC13818-3 standard. In the program map section, the stream_—type is repeated as many times as the number of elements constituting a program specified by the program_—number.

The elementary_—PID is a field for specifying the PID of a transport stream packet which transmits elements constituting a program specified by the program_—number. The elementary_—PID is data described correspondingly to the stream_—type which indicates the type of a stream element.

The ES_—info_—length is data for specifying the number of bytes of a descriptor described following the ES_—info_—length field.

Next, the conditional access table (CAT) is described below in detail with reference toFIGS. 17 and 18. The conditional access table is a section for specifying the PID of a packet which transmits subscription information EMMs used to descramble video data and audio data in a pay broadcast system. The conditional access table is also a section for specifying the relationship between a conditional access system (CA system: Conditional Access System) which allows only subscribers to descramble programs and a subscription information EMM.

The PID of the conditional access table is not specified by the program association table like the program map table and therefore, each field of the conditional access table can be decoded by finding the unique PID value “0x01” assigned to the conditional access table from bit streams.

Specifically, the conditional access table consists of the following: table_—id, section_—syntax_—indicator, section_—length, version_—number, current_—next_—indicator, section_—number, last_—section_—number, and descriptor( ).

The table_—id shows a unique identification number assigned to each table and the table_—id assigned to the conditional access table CAT is “0x01”.

The section_—syntax_—indicator is a constant fixed to “1”. The section_—length is a field for indicating in bytes the length from the bit following this section_—length to the last byte of the CRC section. The version_—number is data for indicating the version number of the conditional access table (CAT). The version_—number is incremented by 1 when any setting of the conditional access table is changed. The current_—next_—indicator is data for indicating whether the transmitted conditional access table is currently available. If the conditional access table is currently available, the current_—next_—indicator is set to “1”; if the conditional access table is not currently available, the current_—next_—indicator is set to “0”.

The section_—number is data for indicating the section number of the conditional access table. For example, the CA_—section( ) field contained in the conditional access table is set to “0x00” to indicate that it is the first section. The section_—number is incremented by 1 each time the sections contained in the conditional access table increase.

The last_—section_—number is data for indicating the section number of the last section among all the sections specified in the conditional access table.

As described above, the descriptor( ) is a data structure used to expand the definitions of programs and program elements. It should be appreciated that in a data transmission device according to the present invention, a data structure of descriptor( ) used in the conditional access table is intended to describe information which specifies the PID of a transport stream packet containing a subscription information EMM.

Next, the conditional access descriptor CA_—descriptor( ) used in the program map table and the conditional access table is described below with reference toFIG. 19.

The conditional access descriptor is used to specify a subscription information EMM containing personal information on subscription and a work key Kw to decipher enciphered ECM data as well as a program decryption information ECM containing a scramble key Ks to descramble elementary streams such as video and audio. Therefore, if elementary streams such as video and audio are scrambled, the conditional access descriptor always exists in the bit streams.

The conditional access descriptor CA_—descriptor( ) consists of the following data: descriptor_—tag, descriptor_—length, CA_—system_—ID, CA_—PID, and private_—data_—byte. The descriptor_—tag is a unique identification tag for identifying each of a plurality of descriptors as described above. The conditional access descriptor CA_—descriptor( ) has a descriptor_—tag of “9” assigned thereto. The descriptor_—length is data for specifying the number of data bytes of a descriptor immediately following the descriptor_—length. The CA_—system_—ID is data for indicating the type of a conditional access system (CA system) which generates and applies associated ECM or EMM data. The CA_—PID indicates the PID of a transport stream containing ECM or EMM data on a conditional access system (CA system) specified by the CA_—system_—ID.

The data contents described in a packet specified by the CA_—PID of the conditional access descriptor CA_—descriptor( ) may vary from context to context of the CA_—descriptor( ). With reference toFIG. 20, a packet specified by the CA_—PID is described below.

It should be appreciated first that the data contents described in a packet specified by the CA_—PID may vary with the usage of the CA_—descriptor( ), that is, whether the CA_—descriptor( ) is used in the conditional access table CAT or in the program map table. Specifically, if the CA_—descriptor( ) exists in the conditional access table, the CA_—PID indicates a transport stream packet containing EMM data. If the CA_—descriptor( ) exists in the program map table, the CA_—PID indicates a transport stream packet containing ECM data.

In addition, the data contents described in a packet specified by the CA_—PID may also vary with the context in the program map table of the conditional access descriptor CA_—descriptor( ). In this regard, the context in the program map table of the conditional access descriptor CA_—descriptor( ) means whether the CA_—descriptor( ) is used in the first FOR statement (FIG. 15) or in the second FOR statement (FIG. 15).

If the conditional access descriptor CA_—descriptor( ) is used in the first FOR statement, the CA_—PID indicates the PID of a transport stream packet containing ECM data. The first CA_—descriptor( ) for this case is used according to the syntax for describing the correspondence between a transport stream packet containing a program specified by the program_—number and a transport stream packet containing ECM data. That is, the same ECM data has been assigned to all data elements contained in the program specified by the program_—number. In other words, all data elements in the program have been scrambled and descrambled with the same scramble key.

On the contrary, if the conditional access descriptor CA_—descriptor( ) is used in the second FOR statement as the second CA_—descriptor( ), the CA_—PID also indicates the PID of a transport stream packet containing ECM data. However, the second CA_—descriptor( ) is not intended to describe the correspondence between a transport stream packet containing a program specified by the program_—number and a transport stream packet containing ECM data but this CA_—descriptor( ) describes the correspondence between a transport stream packet containing data elements specified by the elementary_—PID and a transport stream packet containing ECM data. That is, different ECM data has been assigned to each data element specified by the elementary_—PID. In other words, different data elements in the program have been scrambled and descrambled with different scramble keys. When it is assumed that a program consists of a channel of video data and two channels, that is, main audio and subaudio, of audio data, using different scramble keys for each data element in such a manner may allow the system to scramble the subaudio data with a different scramble key from those for other channels.

Next, EMM data and ECM data are described below.

EMM (Entitlement Management Message) data is data which contains subscription information indicating programs subscribed for by a subscriber and a work key Kw used to encipher a scramble key Ks. EMM data is transmitted in the payload of a transport stream packet like the program association table PAT, the program map table PMT, and the conditional access table CAT. In the following description, a transport stream packet containing EMM data will be referred to as an EMM packet.

As shown inFIG. 21, an EMM packet consists of a header of 4 bytes and a payload section of 183 bytes. Like a transport stream packet as described above, the header of an EMM packet consists of the following data fields: sync_—byte, transport_—error_—indicator, payload_—unit_—start_—indicator, transport_—priority, PID, transport_—scrambling_—control, adaptation_—field_—control, and continuity_—counter. The payload section of 183 bytes consists of an EMM section header, EMM data, CRC, and stuffing bytes.

The EMM section header consists of the following data fields: table_—id, section_—syntax_—indicator, reserved_—0, reserved_—1, section_—length, table_—id_—extention, reserved_—2, version_—number, current_—next_—indicator, section_—number, and last_—section_—number. The table_—id is a unique identification number assigned to each table (each section). The EMM section has user-definable table_—id “0x40” through “0xFE” assigned as identification numbers. The section_—syntax_—indicator is a constant fixed to “1”. The section_—length is a data field for indicating in bytes the length from the bit following this section_—length to the last byte of the CRC section. The table_—id_—extention is data for indicating whether there is any extension data of the EMM section. The version_—number is data for indicating the version number of the EMM section. The version number is incremented when any parameter of the EMM section changes in a transport stream. The current_—next_—indicator is data for indicating whether the transmitted EMM section is currently available. The section_—number is data for indicating the number of the EMM section and it is always “1”. The last_—section_—number is data for indicating the section number of the last section in the EMM section and it is always “1”.

The EMM data consists of the following data fields: card_—ID, EMM_—type, CA_—system_—ID, Kw_—No, Kw, authorize_—type, service_—ID, series_—ID, event_—ID, and component_—map.

The card_—ID is an identification number given to a unique IC card mounted on the IRD and it is also used as an identification number for management of its subscriber. The EMM_—type is data for indicating the type of EMM data. The CA_—system_—ID is an identification number given to a CA system containing a subscriber management system. The Kw indicates a work key used to encipher a scramble key Ks and the Kw_—No is a number for indicating which work key among 256 predefined work keys Kw was used to encipher the scramble key Ks. The authorize_—type, the service_—ID, the series_—ID, and the event_—ID are subscription conditions for indicating which program is subscribed for by a subscriber. The component_—map is data for indicating which element of the subscribed program is subscribed for.

ECM (Entitlement_—Control_—Message) data is data which contains scramble keys Ks used to descramble the scrambled programs subscribed for by a subscriber. ECM data is transmitted in the payload of a transport stream packet like the program association table PAT, the program map table PMT, and the conditional access table CAT. In the following description, a transport stream packet containing ECM data will be referred to as an ECM packet. ECM packets will be transmitted at intervals of approximately 100 msec and scramble keys transmitted as EMM data will be updated at intervals of approximately 4 sec.

As shown inFIG. 22, an ECM packet consists of a header of 4 bytes and a payload section of 183 bytes. Like a transport stream packet as described above, the header of an ECM packet consists of the following data fields: sync_—byte, transport_—error_—indicator, payload_—unit_—start_—indicator, transport_—priority, PID, transport_—scrambling_—control, adaptation_—field_—control, and continuity_—counter. The payload section of 183 bytes consists of an ECM section header, ECM data, CRC, and stuffing bytes.

The ECM section header consists of the following data fields: table_—id, section_—syntax_—indicator, reserved_—0, reserved_—1, section_—length, table_—id_—extention, reserved_—2, version_—number, current_—next_—indicator, section_—number, and last_—section_—number. The table_—id is a unique identification number assigned to each table (each section). The ECM section has user-definable table_—id “0x40” through “0xFE” assigned as identification numbers. The section_—syntax_—indicator is a constant fixed to “1”. The section_—length is a data field for indicating in bytes the length from the bit following this section_—length to the last byte of the CRC section. The table_—id_—extention is data for indicating whether there is any extension data of the ECM section. The version_—number is data for indicating the version number of the ECM section. The version number is incremented when any parameter of the ECM section changes in a transport stream. The current_—next_—indicator is data for indicating whether the transmitted ECM section is currently available. The section_—number is data for indicating the number of the ECM section and it is always “1”. The last_—section_—number is data for indicating the section number of the last section in the ECM section and it is always “1”.

The ECM data consists of the following data fields: ECM_—type, CA_—system_—ID, Kw_—No, service_—mode, service_—ID, series_—ID, event_—ID, component_—map, Ks_—Odd, and Ks_—Even.

The ECM_—type is data for indicating the type of ECM data. The CA_—system_—ID is an identification number given to a CA system containing a subscriber management system. The Kw_—No is a number for indicating which work key among 256 predefined work keys Kw was used to encipher a scramble key Ks. The service_—mode, the service_—ID, the series_—ID, and the event_—ID are subscription conditions for indicating which program is subscribed for by a subscriber. The component_—map is data for indicating which element of the subscribed program is subscribed for. The Ks_—Odd and the Ks_—Even are scramble keys used to scramble transmitted video and audio data. The scramble keys consist of the odd keys Ks_—Odd and the even keys Ks_—Even and the odd keys and the even keys are alternately used as scramble keys at intervals of 4 sec.

Next, the IRD (Integrated_—Receiver_—Decoder)20 provided as a receiver is described below in detail with reference toFIG. 23.

The IRD comprises ademodulation circuit21 for demodulating modulated streams transmitted via a satellite, ademultiplexer22 for dividing the streams demodulated by thedemodulation circuit21 into packet types, aCPU23 for receiving PAT packets, PMT packets, CAT packets, EMM packets, and ECM packets divided by thedemultiplexer22, asecurity module24 for deciphering enciphered work keys Kw′ and enciphered scramble keys Ks′,descramblers25V,25A, and25P for descrambling scrambled video streams, audio streams, and private data streams, anddecoders26V and26A for decoding video streams and audio streams.

Thedemultiplexer22 functions to receive a control command from theCPU23 and supply an appropriate transport stream packet to theCPU23 with a proper timing in response to that command.

TheCPU23 comprises aPAT packet analyzer231 for analyzing PAT packets supplied by thedemultiplexer22, aPMT packet analyzer232 for analyzing PMT packets supplied by thedemultiplexer22, aCAT packet analyzer233 for analyzing CAT packets supplied by thedemultiplexer22, anEMM packet analyzer234 for analyzing EMM′ packets supplied by thedemultiplexer22, and anECM packet analyzer235 for analyzing ECM′ packets supplied by thedemultiplexer22.

ThePAT analyzer231 analyzes a transport stream packet supplied by thedemultiplexer22 as a PAT packet to obtain the program_—number and the program_—map_—PID contained in the PAT packet. ThePAT analyzer231 also receives from thesecurity module24 the authorize_—type indicating which program is subscribed for by a subscriber. Then thePAT analyzer231 compares the authorize_—type supplied by the security module with the program_—number supplied by thedemultiplexer22 and selects only the program_—map_—PID corresponding to the program_—number which is consistent with the program subscribed for by the subscriber. Thus, thePAT analyzer231 can obtain only the PID of a program map table corresponding to that program.

Then thedemultiplexer22 selects a transport stream packet with the PID specified by the program_—map_—PID supplied by thePAT analyzer231 to provide the selected transport stream packet to thePMT analyzer232 as a PMT packet.

ThePMT analyzer232 analyzes PMT data contained in a PMT packet with the PID specified by the program_—map_—PID. Specifically, thePMT analyzer232 obtains from the elementary_—PID described as PMT data in the PMT packet the PID of a transport stream packet containing data elements which constitute a program specified by the program_—number. For example, assuming that a program consists of two data elements, that is, video data and audio data, the first elementary_—PID will specify a transport stream packet containing a video stream and the second elementary_—PID will specify another transport stream packet containing an audio stream.

In addition, thePMT analyzer232 references the CA_—descriptor described in PMT data as a descriptor( ) function. Then thePMT analyzer232 obtains the CA_—PID described in the CA_—descriptor and feeds back this CA_—PID to thedemultiplexer22. The CA_—PID described in the CA_—descriptor is data for indicating the PID of a transport stream packet containing ECM data.

Then thedemultiplexer22 provides a transport stream packet with the PID specified by the elementary_—PID supplied by thePMT analyzer232 to an appropriate processing circuit. For example, if the data element is a video stream, it is provided to thedescrambler25V for descrambling video streams; if the data element is an audio stream, it is provided to thedescrambler25A for descrambling audio streams; if the data element is a private data stream, it is provided to thedescrambler25P for descrambling private data streams.

In addition, thedemultiplexer22 supplies a transport stream packet with the PID specified by the CA_—PID to theECM analyzer235 as an ECM packet. Thus, the ECM data supplied to theECM analyzer235 contains only ECM data concerning a program subscribed for by a subscriber.

TheECM analyzer235 first filters an ECM′ packet received from thedemultiplexer22. Specifically, theECM analyzer235 compares the CA_—system_—ID in the ECM data with the CA_—system_—ID supplied by thesecurity module24 and selects only an ECM packet containing the CA_—system_—ID which matches the CA_—system_—ID supplied by thesecurity module24. Then theECM analyzer235 can obtain enciphered scramble keys Ks′ by analyzing ECM data contained in the selected ECM packet. TheECM analyzer235 supplies the enciphered scramble keys Ks′ to adecryption circuit242 in a microprocessor MPU of thesecurity module24.

Thedemultiplexer22 detects a transport stream packet with the PID of a CAT packet from a transmitted bit stream and provides the detected transport stream packet to theCAT analyzer233 as a CAT packet.

TheCAT analyzer233 detects a CA_—descriptor( ) function contained in the CAT packet received from thedemultiplexer22 and obtains the PID of a transport stream packet specified by the CA_—descriptor( ) of the CAT packet from the CA_—PID in the CA_—descriptor( ) function. The transport stream packet specified by the CA_—descriptor( ) of the CAT packet is a transport stream packet containing EMM information.

Thedemultiplexer22 selects a transport stream packet with the PID specified by the CA_—PID received from theCAT analyzer233 from a transmitted bit stream and supplies the selected transport stream packet to theEMM analyzer234 as an EMM′ packet.

TheEMM analyzer234 first filters an EMM′ packet received from thedemultiplexer22 and selects only an EMM′ packet corresponding to the security module. Specifically, EMM data contained in an EMM′ packet can be obtained by referencing the CA_—PID, because a transport stream packet specified by the CA_—PID of the CA_—descriptor( ) for the EMM packet received from thedemultiplexer22 is an EMM′ packet containing EMM data. TheEMM analyzer234 compares the Card_—ID and the CA_—system_—ID in the EMM data with the Card_—ID and the CA_—system_—ID supplied by amemory241 of thesecurity module24 and selects only an EMM′ packet containing the Card_—ID and the CA_—system_—ID which match the Card_—ID and the CA_—system_—ID supplied by thesecurity module24, respectively.

Then theEMM analyzer234 supplies EMM data of 101 bytes contained in the selected EMM packet to thememory241 of thesecurity module24 as the latest EMM data to replace old EMM data in thememory241. In addition, theEMM analyzer234 supplies an enciphered work key Kw′ contained in the EMM data to thedecryption circuit242 in the microprocessor MPU of thesecurity module24.

Thesecurity module24 consists of thememory241 and the microprocessor comprising thefirst decryption circuit242 and thesecond decryption circuit243. Thesecurity module24 is composed of, for example, an IC card which is removable from the IRD.

Thefirst decryption circuit242 of thesecurity module24 receives an enciphered work key Kw′ from theEMM analyzer234 to decipher the enciphered work key Kw′ with a prestored master key Km. Then thefirst decryption circuit242 supplies the deciphered work key Kw to thesecond decryption circuit243.

Thesecond decryption circuit243 of thesecurity module24 receives an enciphered scramble key Ks′ from theECM circuit235 as well as the deciphered work key Kw from thefirst decryption circuit242 to decipher the enciphered scramble key Ks′ with the deciphered work key Kw. The deciphered scramble key Ks is supplied to thedescramblers25V,25A, and25P. It should be appreciated that in the foregoing, the same scramble key Ks is supplied to thedescramblers25V,25A, and25P but different scramble keys Ks may be supplied to different descramblers if a different scramble key Ks is defined for each data element.

From the foregoing, in a data multiplexing device of such a configuration that transport stream packets of program data which consists of a plurality of data elements are multiplexed and transmitted, a scramble key corresponding to one or more data elements among a plurality of data elements constituting a program is generated and then each data element is scrambled, thereby each data element can be subscribed for by a subscriber.

Since each of multiplexed transport stream packets is scrambled with its corresponding scramble key, the circuit configuration for scrambling can be made simpler than that for scrambling each transport stream packet before multiplexing.

Any overflow from a buffer memory for buffering higher priority data elements can be avoided by switchably controlling a switch means to exclude a buffer memory for buffering lower priority information among a plurality of buffer memories, when the input rate for a data element supplied to each buffer memory is higher than a reference rate.

At the receiver end, different data elements can be descrambled separately by descrambling with a scramble key the transport stream packets of each data element corresponding to that scramble key.

According to the above-mentioned configuration, a data multiplexing device which allows a subscriber to watch and/or hear desired data elements only can be achieved by a simpler implementation.

Moreover, any overflow from a buffer memory can be avoided effectively by excluding lower priority data elements from the selections and multiplexing desired data elements in preference to others.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a digital broadcast system which performs compression-coding of video data and audio data according to the MPEG2 and transmits the coded streams over a ground wave or a satellite wave.

Claims (80)

1. A program distribution system for distributing a program consisting of a plurality of data elements, said program distribution system comprising:

a subscriber management system for managing subscribers' subscriptions for each program or data element;

a subscriber authorization system for generating a scramble key to be used for descrambling said data elements contained in said program for each of said data elements; and

a multiplexer system comprising:

an encoding system for encoding each of said data elements contained in said program to generate encoded streams consisting of encoded data elements for each program;

a multiplexing means for multiplexing said encoded streams generated for each program by said encoding system; and

a scramble means for selectively scrambling each of said encoded data elements contained in said multiplexed stream based on said scramble key generated by said subscriber authorization system,

wherein said subscriber management system generates a work key for enciphering said scramble key,

wherein said subscriber authorization system comprises a first encryption means for enciphering said work key supplied as EMM data with a master key to provide an enciphered work key as an output,

wherein said multiplexer system comprises a second encryption means for enciphering said scramble key contained in ECM data with said work key to provide an enciphered scramble key as an output, and

wherein said work key used by said second encryption means for enciphering said scramble key is not said enciphered work key contained in said EMM data but an unenciphered work key obtained from a work key table supplied by said subscriber authorization system.

2. A program distribution system according toclaim 1, wherein said second encryption means obtains said work key from a work key identification number contained in said ECM data by referencing said work key table supplied by said subscriber authorization system, and

said second encryption means provides said enciphered scramble key enciphered by said second encryption means as enciphered ECM data.

3. A program distribution system according toclaim 2, wherein said encoded stream provided by said encoding system and enciphered EMM data and ECM data provided by said subscriber authorization system are provided in the form of transport stream packets and each of said transport stream packets is given a packet ID for identifying said transport stream packet.

4. A program distribution system according toclaim 3, wherein said second encryption means provides enciphered ECM data as an output to said multiplexing means.

5. A program distribution system according toclaim 4, wherein said scramble means scrambles only said plurality of data elements constituting said program.

6. A program distribution system according toclaim 4, wherein said scramble means scrambles said data elements by using scramble keys associated with said data elements based on a table which shows the correspondence between the packet ID of a transport stream packet containing each of said data elements and a scramble key defined for said data element.

7. A program distribution system according toclaim 4, wherein said scramble means detects the packet IDs of all transport stream packets supplied by said multiplexing means to said scramble means,

said scramble means determines whether scramble keys are defined for said detected packet IDs based on a table which shows the correspondence between said packet IDs and said scramble keys,

if some scramble keys are defined for said packet IDs, said scramble means scrambles data elements contained in transport stream packets indicated by said packet IDS with said defined scramble keys, and

if no scramble keys are defined for said packet IDs, said scramble means does not scramble data contained in transport stream packets indicated by said packet IDs.

8. A program distribution system according toclaim 2, wherein said multiplexer system further comprises a buffer means for buffering data supplied to said multiplexer system in the form of transport stream packets and for providing said transport stream packets to said multiplexing means.

9. A program distribution system according toclaim 8, wherein said multiplexer system monitors free area of a plurality of buffers for buffering said transport stream packets containing said data elements, and

if any of said plurality of buffers for buffering said transport stream packets containing said data elements is likely to overflow, said transport stream packets containing said EMM data are not provided to said multiplexing means by a buffer for buffering said transport stream packets containing said EMM data and instead, said transport stream packets containing said data elements are provided to said multiplexing means by said buffer likely to overflow.

10. A program distribution system according toclaim 2, further comprising:

a distribution system for distributing transport streams provided by said multiplexer system to the receiving end through a transmission line; and

a reception system for receiving said transport streams transmitted through said transmission line.

11. A program distribution system according toclaim 10, wherein said reception system comprises:

a demultiplexer for demultiplexing said transmitted transport streams;

a descrambler for descrambling said scrambled data elements with said supplied scramble keys, respectively;

a decoder for decoding said descrambled data for each data element;

a CPU for analyzing transport stream packets constituting said transport stream; and

a security module for deciphering said enciphered scramble key contained in said transport stream and supplying said deciphered scramble key to said descrambler.

12. A program distribution system according toclaim 11, wherein said security module comprises:

a memory means for storing a subscriber's subscription information contained in said enciphered EMM data contained in said transmitted transport stream;

a first decryption means for receiving said enciphered work key contained in said transmitted transport stream as well as the same master key as that used by said subscriber management system to decipher said enciphered work key with said master key; and

a second decryption means for receiving said enciphered scramble key contained in said transport stream as well as said deciphered work key supplied by said first decryption means to decipher said enciphered scramble key with said deciphered work key.

13. A program distribution system according toclaim 12, wherein said CPU filters, from said transport stream packets containing said enciphered ECM data supplied by said demultiplexer, only a transport stream packet having enciphered ECM data on a program or data element subscribed for by a subscriber, and

said CPU obtains said enciphered scramble key from said enciphered ECM data by analyzing said enciphered ECM data contained in said filtered transport stream packet.

14. A program distribution system according toclaim 13, wherein if an enciphered scramble key associated with said program is supplied by said CPU, said security module deciphers said supplied enciphered scramble key to supply the same scramble key to a plurality of descramblers corresponding to a plurality of data elements constituting said program, respectively, and

if a plurality of enciphered scramble keys associated with said plurality of data elements are supplied by said CPU, said security module deciphers said plurality of supplied enciphered scramble keys, respectively, to supply different scramble keys to a plurality of descramblers corresponding to subscribed data elements among said plurality of data elements.

15. A program distribution system for distributing a program consisting of a plurality of data elements, said program distribution system comprising:

a subscriber management system for managing subscribers' subscriptions for each program or data element;

a subscriber authorization system for generating a scramble key to be used for descrambling said data elements contained in said program for each of said data elements; and

a multiplexer system comprising:

an encoding system for encoding each of said data elements contained in said program to generate encoded streams consisting of encoded data elements for each program;

a multiplexing means for multiplexing said encoded streams generated for each program by said encoding system; and

a scramble means for selectively scrambling each of said encoded data elements contained in said multiplexed stream based on said scramble key generated by said subscriber authorization system,

wherein said subscriber authorization system comprises a first encryption means for enciphering with a master key a work key used for enciphering said scramble key,

said subscriber authorization system supplies to said multiplexer system said enciphered work key enciphered by said first encryption means and a subscriber identification number for identifying said subscriber as enciphered EMM data,

wherein said multiplexer system further comprises, previous to said multiplexing means, a second encryption means for enciphering a scramble key contained in ECM data,

wherein said second encryption means obtains a work key from a work key identification number contained in said ECM data by referencing said work key table,

said second encryption means enciphers said scramble key contained in said ECM data by using said work key obtained from said work key table, and

said second encryption means supplies to said multiplexing means said enciphered scramble key enciphered by said second encryption means as enciphered ECM data.

16. A program distribution system according toclaim 15, further comprising:

an encoder/multiplexer control system which generates a program specific information for identifying packet IDs of a transport stream packet containing said plurality of data elements constituting said program, a transport stream packet containing said ECM data, and a transport stream packet containing said EMM data within a transport stream provided by said data distribution system, and

wherein the encoder/multiplexer control system multiplexes said transport stream packet containing said plurality of data elements constituting said program, said transport stream packet containing said ECM data, and said transport stream packet containing said EMM data according to said program specific information.

17. A program distribution system according toclaim 16, wherein said encoder/multiplexer control system assigns to all transport stream packets supplied to said multiplexer system in the form of transport stream packets, packet IDs for identifying said transport stream packets.

18. A program distribution system according toclaim 17, wherein said program specific information consists of at least a program association table, a program map table, and a conditional access table.

19. A program distribution system according toclaim 18, wherein said encoder/multiplexer control system supplies to said multiplexer system a transport stream packet containing said program association table as a PAT packet,

said encoder/multiplexer control system supplies to said multiplexer system a transport stream packet containing said program map table as a PMT packet, and

said encoder/multiplexer control system supplies to said multiplexer system a transport stream packet containing said conditional access table as a CAT packet.

20. A program distribution system according toclaim 19, wherein said program association table is a table for specifying a program number and the packet ID of a PMT packet corresponding to said program number,

said program map table is a table for specifying the packet ID of a transport stream packet containing each of a plurality of data elements constituting a program, and

said conditional access table is a table for specifying the packet ID of an enciphered EMM packet.

21. A program distribution system according toclaim 20, wherein said program association table describes the program number for indicating a program and the packet ID of a PMT packet associated with said program, and

said program map table describes the program number for indicating said program, a plurality of packet IDs containing transport stream packets containing a plurality of data elements constituting said program, and a descriptor for specifying the packet ID of an enciphered ECM packet associated with said program or said data element.

22. A program distribution system according toclaim 21, wherein if said descriptor in said program map table is described at a location corresponding to said program number, said descriptor specifies the packet ID of an ECM packet containing a scramble key for scrambling all data elements of said plurality of data elements constituting said program, and

if said descriptor in said program map table is described at a location corresponding to each of said data elements of said program, said descriptor specifies the packet IDs of a plurality of ECM packets containing a plurality of scramble keys for scrambling said plurality of data elements constituting said program, respectively.

23. A program distribution system according toclaim 22, wherein if said program has a first data element through an n'th data element and the same scramble key is specified for said first data element through said n'th data element,

said program map table describes the correspondence between the program number for indicating said program and the packet IDs of ECM packets containing scramble keys for scrambling said first data element through said n'th data element, respectively.

24. A program distribution system according toclaim 22, wherein if said program has a first data element through an n'th data element and at least one different scramble key is specified for said first data element through said n'th data element,

said program map table describes the correspondence between the packet ID of a transport stream packet containing said first data element and the packet ID of a transport stream packet containing ECM data containing a scramble key for scrambling said first data element, and

said program map table describes the correspondence between the packet ID of a transport stream packet containing said n'th data element and the packet ID of a transport stream packet containing ECM data containing a scramble key for scrambling said n'th data element.

25. A program distribution system according toclaim 19, wherein said encoder/multiplexer control system specifies unique packet IDs for said program map table and said conditional access table.

26. A program distribution system according toclaim 19, wherein said scramble means does not scramble said program specific information, said EMM data, and said ECM data but scrambles only said data elements.

27. A program distribution system according toclaim 19, wherein said scramble means scrambles said data elements by using scramble keys specified for said data elements based on a table which shows the correspondence between the packet ID of a transport stream packet containing each of said data elements and a scramble key specified for said data element.

28. A program distribution system according toclaim 19, wherein said encoder/multiplexer control system stores packet IDs used for previous operations so that repetitive assignment at a packet ID to a plurality of transport stream packets can be avoided when packet IDs are specified to identify said ECM packet, said EMM packet, said PSI packet, and said elementary packet, respectively.

29. A program distribution system according toclaim 19, wherein said encoder/multiplexer control system generates a table which shows the correspondence between the packet ID assigned to each transport stream packet and a scramble key used for scrambling data contained in said transport stream packet, and

said encoder/multiplexer control system supplies to said multiplexer system said table for showing the correspondence between said packet IDs and said scramble keys.

30. A program distribution system according toclaim 29, wherein said scramble means does not scramble said program specific information, said EMM data, and said ECM data but scrambles only said data elements by referencing said table for showing the correspondence between said packet IDs and said scramble keys.

31. A program distribution system according toclaim 29, wherein said scramble means scrambles said data elements with scramble keys specified for said data elements by referencing said table for showing the correspondence between said packet IDs and said scramble keys.

32. A program distribution system according toclaim 29, wherein said scramble means detects the packet IDs of all transport stream packets supplied by said multiplexing means to said scramble means,

said scramble means determines whether scramble keys are defined for said detected packet IDs based an said table which shows the correspondence between said packet IDs and said scramble keys,

if some scramble keys are defined for said packet IDs, said scramble means scrambles data elements contained in transport stream packets indicated by said packet IDs with said defined scramble keys, and

if no scramble keys are defined for said packet IDs, said scramble means does not scramble data contained in transport stream packets indicated by said packet IDs.

33. A program distribution system according toclaim 15, wherein said multiplexer system further comprises:

a plurality of buffer means for buffering PAT packets, PMT packets, CAT packets, transport stream packets containing said data elements, enciphered EMM packets, and enciphered ECM packets, respectively, and for providing said transport stream packets to said multiplexing means.

34. A program distribution system according toclaim 33, wherein said multiplexer system monitors free area of a plurality of buffers for buffering said transport stream packets containing said data elements, and

if any of said plurality of buffers for buffering said transport stream packets containing said data elements is likely to overflow, said EMM packets are not provided to said multiplexing means by a buffer for buffering said EMM packets and instead, said transport stream packets containing said data elements are provided to said multiplexing means by said buffer likely to overflow.

35. A program distribution system according toclaim 24, further comprising:

a distribution system for distributing transport streams provided by said multiplexer system to the receiving end through a transmission line, and

a reception system for receiving said transport streams transmitted through said transmission line.

36. A program distribution system according toclaim 35, wherein said reception system comprises:

a demultiplexer for demultiplexing said transmitted transport streams;

a descrambler for descrambling said scrambled data elements with said supplied scramble keys, respectively;

a decoder for decoding said descrambled data for each data element;

a CPU for analyzing transport stream packets constituting said transport stream; and

a security module for deciphering said enciphered scramble key contained in said transport stream and supplying said deciphered scramble key to said descrambler.

37. A program distribution system according toclaim 36, wherein said CPU comprises:

a PAT analyzing means for analyzing a program association table contained in said transport stream;

a PMT analyzing means for analyzing a program map table contained in said transport stream;

a CAT analyzing means for analyzing a conditional access table contained in said transport stream;

an EMM analyzing means for analyzing enciphered EMM data contained in said transport stream; and

an ECM analyzing means for analyzing enciphered ECM data contained in said transport stream.

38. A program distribution system according toclaim 36, wherein said security module comprises:

a memory means for storing a subscriber's subscription information contained in said EMM data;

a first decryption means for receiving said enciphered work key contained in said transmitted transport stream as well as the same master key as that used by said subscriber management system to decipher said enciphered work key with said master key; and

a second decryption means for receiving said enciphered scramble key contained in said transport stream as well as said deciphered work key supplied by said first decryption means to decipher said enciphered scramble key with said deciphered work key.

39. A program distribution system according toclaim 38, wherein said CPU identifies a transport stream packet containing each of data elements constituting said program by analyzing a program association table and a program map table contained in said transport stream and controls said demultiplexer to provide said transport stream packet containing said data element to appropriate one of said scramblers.

40. A program distribution system according toclaim 39, wherein said CPU detects a transport stream packet containing EMM data by analyzing a conditional access table contained in said transport stream,

said CPU filters, from said transport stream containing said EMM data, only a transport stream packet having EMM data on a program subscribed for by a subscriber, and

said CPU obtains said enciphered work key from said EMM data by analyzing said EMM data contained in said filtered transport stream packet.

41. A program distribution system according toclaim 38, wherein said CPU detects transport stream packets containing a plurality of data elements constituting said program and said ECM data, respectively, by analyzing a program association table contained in said transport stream and a program map table specified by said program association table, and

said CPU controls said demultiplexer to supply said transport stream packets containing said plurality of data elements to said descramblers, respectively, and to receive said transport stream packet containing said ECM data.

42. A program distribution system according toclaim 41, wherein said CPU filters, from said transport stream packets containing said enciphered ECM data supplied by said demultiplexer, only a transport stream packet having enciphered ECM data on a program or data element subscribed for by a subscriber, and

said CPU obtains said enciphered scramble key from said enciphered ECM data by analyzing said enciphered ECM data contained in said filtered transport stream packet.

43. A program distribution system according toclaim 42, wherein if the correspondence between said program number and the packet ID of said enciphered ECM packet is described according to the syntax of said program map table,

said CPU supplies to said security module an enciphered scramble key contained in said enciphered ECM packet specified by said packet ID as an enciphered scramble key corresponding to said program, and

if the correspondence between a plurality of data elements constituting said program and the packet IDs of said plurality of enciphered ECM packets is described according to the syntax of said program map table,

said CPU supplies to said security module a plurality of different scramble keys contained in said enciphered ECM packets specified by said plurality of packet IDs as enciphered scramble keys corresponding to said plurality of data elements.

44. A program distribution system according toclaim 43, wherein if an enciphered scramble key associated with said program is supplied by said CPU, said security module deciphers said supplied enciphered scramble key to supply the same scramble key to a plurality of descramblers corresponding to a plurality of data elements constituting said program, respectively, and

if a plurality of enciphered scramble keys associated with said plurality of data elements are supplied by said CPU, said security module deciphers said plurality of supplied enciphered scramble keys, respectively, to supply different scramble keys to a plurality of descramblers corresponding to subscribed data elements among said plurality of data elements.

45. A program transmission method for transmitting a program consisting of a plurality of data elements, said method comprising:

a scramble key generation step for generating a plurality of scramble keys to be used for scrambling a plurality of data elements contained in said program so that a subscriber can watch and/or hear only programs or data elements subscribed for by said subscriber;

an encoding step for encoding each of said data elements contained in said program to generate encoded streams consisting of encoded data elements for each program;

a multiplexing step for multiplexing said encoded streams provided for each program by said encoding step; and

a scramble step for selectively scrambling each of said encoded data elements contained in said multiplexed stream based on said generated scramble key,

wherein said multiplexing step comprises an encryption step for enciphering a scramble key contained in ECM data,

wherein said scramble key generation step generates a work key table which shows the correspondence between said work key and a work key identification number for identifying said work key,

wherein said encryption step in said multiplexing step obtains a work key from said work key identification number contained in said ECM data by referencing said work key table,

said encryption step enciphers said scramble key contained in said ECM data by using said work key obtained from said work key table, and

said encryption step provides said enciphered scramble key enciphered by said second encryption circuit as enciphered ECM data.

46. A program transmission method according toclaim 45, further comprising a program specific information generation step for assigning to all transport stream packets, packet IDs for identifying said transport stream packets.

47. A program transmission method according toclaim 46, wherein said program specific information consists of at least a program association table, a program map table, and a conditional access table.

48. A program transmission method according toclaim 47, wherein said program specific information generation step supplies to said multiplexing step a transport stream packet containing said program association table as a PAT packet,

said program specific information generation step supplies to said multiplexing step a transport stream packet containing said program map table as a PMT packet, and

said program specific information generation step supplies to said multiplexing step a transport stream packet containing said conditional access table as a CAT packet.

49. A program transmission method according toclaim 48, wherein said program association table is a table for specifying a program number and the packet ID of a PMT packet corresponding to said program number,

said program map table is a table for specifying the packet ID of a transport stream packet containing each of a plurality of data elements constituting a program, and

said conditional access table is a table for specifying the packet ID of said enciphered EMM packet.

50. A program transmission method according toclaim 49, wherein said program association table describes the program number for indicating a program and the packet ID of a PMT packet associated with said program, and

said program map table describes the program number for indicating said program, a plurality of packet IDs containing transport stream packets containing a plurality of data elements constituting said program, and a descriptor for specifying the packet ID of an enciphered ECM packet associated with said program or said data element.

51. A program transmission method according toclaim 50, wherein if said descriptor in said program map table is described at a location corresponding to said program number, said descriptor specifies the packet ID of an ECM packet containing a scramble key for scrambling all data elements of said plurality of data elements constituting said program, and

if said descriptor in said program map table is described at a location corresponding to each of said data elements of said program, said descriptor specifies the packet IDs of a plurality of ECM packets containing a plurality of scramble keys for scrambling said plurality of data elements constituting said program, respectively.

52. A program transmission method according toclaim 51, wherein if said program has a first data element through an n'th data element and at least one different scramble key is specified for said first data element through said n'th data element,

said program map table describes the correspondence between the packet ID of a transport stream packet containing said first data element and the packet ID of a transport stream packet containing ECM data containing a scramble key for scrambling said first data element, and

said program map table describes the correspondence between the packet ID of a transport stream packet containing said n'th data element and the packet ID of a transport stream packet containing ECM data containing a scramble key for scrambling said n'th data element.

53. A program transmission method according toclaim 48, wherein said scramble step does not scramble said program specific information, EMM data, and said ECM data but scrambles only said data elements by using scramble keys specified for said data elements based on a table which shows the correspondence between the packet ID of a transport stream packet containing each of said data elements and a scramble key specified for said data element.

54. A program transmission method according toclaim 48, wherein said program specific information generation step generates a table which shows the correspondence between the packet ID assigned to each transport stream packet and a scramble key used for scrambling data contained in said transport stream packet, and

said program specific information generation step supplies to said multiplexing step said table for showing the correspondence between said packet IDs and said scramble keys.

55. A program transmission method according toclaim 54, wherein said scramble means does not scramble said program specific information, EMM data, and said ECM data but scrambles only said data elements by referencing said table for showing the correspondence between said packet IDs and said scramble keys.

56. A program transmission method according toclaim 54, wherein said scramble step detects the packet IDs of all transport stream packets supplied by said multiplexing means to said scramble means,

said scramble step determines whether scramble keys are defined for said detected packet IDs based on said table which shows the correspondence between said packet IDs and said scramble keys,

if some scramble keys are defined for said packet IDs, said scramble step scrambles data elements contained in transport stream packets indicated by said packet IDs with said defined scramble keys, and

if no scramble keys are defined for said packet IDs, said scramble step does not scramble data contained in transport stream packets indicated by said packet IDs.

57. A program transmission method according toclaim 45, wherein said multiplexing step enciphers said scramble keys with said work key, and

said multiplexing step buffers PAT packets, PMT packets, CAT packets, transport stream packets containing said data elements, EMM packets, and ECM packets in a plurality of buffer means, respectively.

58. A program transmission method according toclaim 57, wherein said multiplexing step monitors free area of a plurality of buffers for buffering said transport stream packets containing said data elements, and

if any of said plurality of buffers for buffering said transport stream packets containing said data elements is likely to overflow, said EMM packets are not provided to said multiplexing step by a buffer for buffering said EMM packets and instead, said transport stream packets containing said data elements are provided by said buffer likely to overflow.

59. A conditional access system for providing a conditional access to only subscribed programs and data elements among a plurality of programs and a plurality of data elements constituting said programs distributed by a program distribution system:

wherein said program distribution system comprises:

a subscriber authorization system for generating a plurality of scramble keys to be used for scrambling data elements contained in said program so that a subscriber can watch and/or hear only data programs or elements subscribed for by said subscriber,

wherein said subscriber authorization system comprises a first encryption means for enciphering a work key used for enciphering said scramble key with a master key;

said conditional access system comprising:

a demultiplexer means for demultiplexing, from a transport stream, a transport stream packet containing a plurality of the scrambled data elements constituting said program and for demultiplexing a plurality of transport stream packets containing a plurality of enciphered scramble keys associated with said plurality of data elements;

a filter means for filtering, from said plurality of transport stream packets containing said plurality of demultiplexed enciphered scramble keys, a transport stream packet containing an enciphered scramble key associated with said programs and data elements subscribed for by a subscribers;

a decryption means for deciphering said plurality of enciphered scramble keys contained in said plurality of filtered transport stream packets to generate a plurality of deciphered scramble keys;

a descramble means for descrambling said plurality of demultiplexed data elements for each data element by using said plurality of deciphered scramble keys associated with said plurality of data elements;

a decoding means for decoding said plurality of data elements descrambled by said descramble means; and

a multiplexer system having a second encryption means for enciphering a scramble key contained in ECM data,

wherein said subscriber authorization system supplies to said second encryption means of said multiplexer system a work key table which shows the correspondence between said work key and a work key identification number for identifying said work key,

wherein said second encryption means obtains a work key from said work key identification number contained in said ECM data by referencing said work key table,

said second encryption means enciphers said scramble key contained in said ECM data by using said work key obtained from said work key table, and

said second encryption means supplies to said multiplexing system said enciphered scramble key enciphered by said second encryption means as enciphered ECM data.

60. A conditional access system according toclaim 59, further comprising an encoder/multiplexer control system that assigns to all transport stream packets supplied to said multiplexer system in the form of transport stream packets, packet IDs for identifying said transport stream packets.

61. A conditional access system according toclaim 60, further comprising program specific information that consists of at least a program association table, a program map table, and a conditional access table.

62. A conditional access system according toclaim 61, wherein said encoder/multiplexer control system supplies to said multiplexer system a transport stream packet containing said program association table as a PAT packet,

said encoder/multiplexer control system supplies to said multiplexer system a transport stream packet containing said program map table as a PMT packet, and

said encoder/multiplexer control system supplies to said multiplexer system a transport stream packet containing said conditional access table as a CAT packet.

63. A conditional access system according toclaim 62, wherein said program association table is a table for specifying a program number and the packet ID of a PMT packet corresponding to said program number,

said program map table is a table for specifying the packet ID of a transport stream packet containing each of a plurality of data elements constituting a program, and

said conditional access table is a table for specifying the packet ID of an enciphered EMM packet.

64. A conditional access system according toclaim 63, wherein said program association table describes the program number for indicating a program and the packet ID of a PMT packet associated with said program, and

said program map table describes the program number for indicating said program, a plurality of packet IDs containing transport stream packets containing a plurality of data elements constituting said program, and a descriptor for specifying the packet ID of an enciphered ECM packet associated with said program or said data element.

65. A conditional access system according toclaim 64, wherein if said descriptor in said program map table is described at a location corresponding to said program number, said descriptor specifies the packet ID of an ECM packet containing a scramble key for scrambling all data elements of said plurality of data elements constituting said program, and

if said descriptor in said program map table is described at a location corresponding to each of said data elements of said program, said descriptor specifies the packet IDs of a plurality of ECM packets containing a plurality of scramble keys for scrambling said plurality of data elements constituting said program, respectively.

66. A conditional access system according toclaim 65, wherein if said program has a first data element through an n'th data element and at least one different scramble key is specified for said first data element through said n'th data element,

said program map table describes the correspondence between the packet ID of a transport stream packet containing said first data element and the packet ID of a transport stream packet containing ECM data containing a scramble key for scrambling said first data element, and

said program map table describes the correspondence between the packet ID of a transport stream packet containing said n'th data element and the packet ID of a transport stream packet containing ECM data containing a scramble key for scrambling said n'th data element.

67. A conditional access system according toclaim 62, wherein said scramble means does not scramble said program specific information, EMM data, and said ECM data but scrambles only said data elements by using scramble keys specified for said data elements based on a table which shows the correspondence between the packet ID of a transport stream packet containing each of said data elements and a scramble key specified for said data element.

68. A conditional access system according toclaim 62, wherein said encoder/multiplexer control system generates a table which shows the correspondence between the packet ID assigned to each transport stream packet and a scramble key used for scrambling data contained in said transport stream packet, and

said encoder/multiplexer control system supplies to said multiplexer system said table for showing the correspondence between said packet IDs and said scramble keys.

69. A conditional access system according toclaim 68, wherein said scramble means does not scramble said program specific information, EMM data, and said ECM data but scrambles only said data elements by referencing said table for showing the correspondence between said packet IDs and said scramble keys.

70. A conditional access system according toclaim 68, wherein said scramble means detects the packet IDs of all transport stream packets supplied by said to said scramble means,

said scramble means determines whether scramble keys are defined for said detected packet IDs based on said table which shows the correspondence between said packet IDs and said scramble keys,

if some scramble keys are defined for said packet IDs, said scramble means scrambles data elements contained in transport stream packets indicated by said packet IDs with said defined scramble keys, and

if no scramble keys are defined for said packet IDs, said scramble means does not scramble data contained in transport stream packets indicated by said packet IDs.

71. A conditional access system according toclaim 59, wherein said multiplexer system further comprises:

a plurality of buffer means for buffering PAT packets, PMT packets, CAT packets, transport stream packets containing said data elements, enciphered EMM packets, and enciphered ECM packets, respectively, and for providing said transport stream packets to said multiplexing system.

72. A conditional access system according toclaim 71, wherein said multiplexer system monitors free area of a plurality of buffers for buffering said transport stream packets containing said data elements, and

if any of said plurality of buffers for buffering said transport stream packets containing said data elements is likely to overflow, said EMM packets are not provided to said multiplexing system by a buffer for buffering said EMM packets and instead, said transport stream packets containing said data elements are provided to said multiplexing means system by said buffer likely to overflow.

73. A conditional access system according toclaim 70, wherein said filter means comprises:

a PAT analyzing means for analyzing a program association table contained in said transport stream;

a PMT analyzing means for analyzing a program map table contained in said transport stream;

a CAT analyzing means for analyzing a conditional access table contained in said transport stream;

an EMM analyzing means for analyzing enciphered EMM data contained in said transport stream; and

an ECM analyzing means for analyzing enciphered ECM data contained in said transport stream.

74. A conditional access system according toclaim 70, wherein said decryption means comprises:

a memory means for storing a subscriber's subscription information contained in said EMM data;

a first decryption means for receiving said enciphered work key contained in said transmitted transport stream as well as the same master key as that used by said subscriber management system to decipher said enciphered work key with said master key; and

a second decryption means for receiving said enciphered scramble key contained in said transport stream as well as said deciphered work key supplied by said first decryption means to decipher said enciphered scramble key with said deciphered work key.

75. A conditional access system according toclaim 74, wherein said demultiplexer means and said filter means identify a transport stream packet containing each of data elements constituting said program by analyzing a program association table and a program map table contained in said transport stream and control said demultiplexer to provide said transport stream packet containing said data element to appropriate one of said scramblers.

76. A conditional access system according toclaim 75, wherein said demultiplexer means and said filter means detect a transport stream packet containing EMM data by analyzing a conditional access table contained in said transport stream,

said demultiplexer means and said filter means filter, from said transport stream containing said EMM data, only a transport stream packet having EMM data on a program subscribed for by a subscriber, and

said demultiplexer means and said filter means obtain said enciphered work key from said EMM data by analyzing said EMM data contained in said filtered transport stream packet.

77. A conditional access system according toclaim 74, wherein said demultiplexer means and said filter means detect transport stream packets containing a plurality of data elements constituting said program and said ECM data, respectively, by analyzing a program association table contained in said transport stream and a program map table specified by said program association table, and

said demultiplexer means and said filter means control said demultiplexer to supply said transport stream packets containing said plurality of data elements to said descramblers, respectively, and to receive said transport stream packet containing said ECM data.

78. A conditional access system according toclaim 77, wherein said demultiplexer means and said filter means filter, from said transport stream packets containing said enciphered ECM data supplied by said demultiplexer, only a transport stream packet having enciphered ECM data on a program or data element subscribed for by a subscriber, and

said demultiplexer means and said filter means obtain said enciphered scramble key from said enciphered ECM data by analyzing said enciphered ECM data contained in said filtered transport stream packet.

79. A conditional access system according toclaim 78, wherein if the correspondence between said program number and the packet ID of said enciphered ECM packet is described according to the syntax of said program map table,

said filter means supplies to said decryption means an enciphered scramble key contained in said enciphered ECM packet specified by said packet ID as an enciphered scramble key corresponding to said program, and

if the correspondence between a plurality of data elements constituting said program and the packet IDs of said plurality of enciphered ECM packets is described according to the syntax of said program map table,

said filter means supplies to said decryption means a plurality of different scramble keys contained in said enciphered ECM packets specified by said plurality of packet IDs as enciphered scramble keys corresponding to said plurality of data elements.

80. A conditional access system according toclaim 79, wherein if an enciphered scramble key associated with said program is supplied by said filter means, said decryption means deciphers said supplied enciphered scramble key to supply the same scramble key to a plurality of descramblers corresponding to a plurality of data elements constituting said program, respectively, and

if a plurality of enciphered scramble keys associated with said plurality of data elements are supplied by said filter means, said decryption means deciphers said plurality of supplied enciphered scramble keys, respectively, to supply different scramble keys to a plurality of descramblers corresponding to subscribed data elements among said plurality of data elements.

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